Get on the bed in a ‘slightly reclined’ position supported by pillows behind your head and lower back.
Firstly, straighten your knee by sliding your foot down the bed sheet (first image).
Then bend your knee by pulling your heel along the sheet towards your bottom (second image).
Try to keep your leg straight and do not let it ‘roll’ out.
You may find it helpful to use a cord or rope to help you bring your leg up, and a plastic bag under your foot to allow it to slide on the bed easily.
Repeat 10 times.